1. Field of the Invention
The present invention relates to a method of making a three-dimensional object by sintering and curing a powder material by irradiating an optical beam thereon.
2. Description of the Related Art
The three-dimensional object is made in such a manner that cross-sectional data of plural layers that are sliced in a desired layer thickness are obtained from design data (CAD data) of the three-dimensional object, a scanning outline shape is calculated on the basis of the cross section data of these layers, and a plurality of layers is united in a three dimension to be sintered and cured by repeating irradiation of an optical beam on a powder material and curing of this powder material. Accordingly, a method of making the three-dimensional object is characterized in that, without so-called CAM (Computer aided manufacturing) apparatus, the three-dimensional object in an arbitrary shape can be made, and further, compared to a making method such as cutting process or the like, the three-dimensional object in a desired shape can be made more rapidly.
Japanese Patent No. 2620353 discloses a method of making a three-dimensional object, which is known as an optical formation method. According to the making method disclosed in Japanese Patent No. 2620353, by irradiating the optical beam on a predetermined portion of the powder material, a sintered layer, on which the powder material is sintered, is formed, and by repeating the formation of the powder material layer and the sintered layer, the three-dimensional object is made. According to this method, by performing a removing step for removing an excess portion from a surface of laminated provisional three-dimensional object only once, the three-dimensional object having the desirable shape has been made finally.
By the way, upon irradiating the optical beam and sintering the powder material, a heat generated by the irradiation of the optical beam is used. The generated heat is transmitted to a periphery of the sintered portion, so that the periphery has been also heated to a high temperature. Since the periphery portion that is heated to a high temperature has a high reactivity, the powder material at the periphery tends to attach to the periphery portion. If the powder material attaches to the periphery portion, this attached powder material changes its nature into an accretion in a low density by its heat. In order to gain the three-dimensional object having a smooth surface, it is necessary to remove the accretion in a low density.
Therefore, the present applicant suggests a following making method in JP-A-2000-306546. In other words, a making method disclosed in JP-A-2000-306546 includes the steps of forming a powder material layer; irradiating an optical beam on a predetermined portion of the powder material layer and sintering the powder material of the predetermined portion thereof to form a sintered layer; repeating these steps to form a sintered block united with a plurality of the sintered layers; removing an excess portion from a surface of the sintered block to have a desired outline shape; and repeating the power material layer forming step and the sintered layer forming step with respect to the sintered block from which the excess portion is removed. In other words, the present applicant suggests a method, whereby a lower sintered block united with a plurality of sintered layers is formed, the excess portion is cut and removed from the lower sintered block, and then, a first sintered layer of the next upper sintered block is formed. According to this method, by repeating the sintered block forming step and the step of cutting and removing an excess portion at the sintered block, without a restriction such as a length of an industrial tool, it is possible to smoothly finish a surface of the three-dimensional object.
However, the above-described method having a step of cutting and removing the excess portion from the sintered block also involves a following problem.
In other words, as shown in FIG. 14, at first, from a lower sintered block B united with a plurality of sintered layers, the excess portion on the surface and the side thereof is removed by using a cutting tool 41 or the like. In the next place, when forming an upper sintered block B+1, by which the lower sintered block B is to be united with a plurality of sintered layers on its surface, with respect to the outside surface of the lower sintered block B, from which the excess portion has been removed and has a smooth finished surface, the excess powder material at the periphery thereof is attached and sintered. As a result, an excess sintered portion 17 hanging like an icicle is formed. Then, even if the excess portion is cut and removed from the sintered block B+1 on the excess sintered portion 17 by using the cutting tool 41 or the like, this excess sintered portion 17 is not removed and is left. Therefore, on the outer surface of the accomplished three-dimensional object, regularities due to the excess sintered portion 17 are formed.
Needless to say, upon removing the excess sintered portion 17 of the upper sintered block B+1, it is technically possible to remove the excess sintered portion 17 that is formed on the outside surface of an upper part of the lower sintered block B. However, in this case, an area to be removed becomes large, and it takes a long time to remove the excess sintered portion 17. Then, since a removing and processing time for removing each of the excess sintered portion 17 on a plurality of sintered blocks is increased, total of the removing and processing time has been increased significantly.